1. Field of the Invention
The present invention relates to a magnetic disk drive in which the rotation of the spindle motor is halted or stopped for the purpose of achieving lower power consumption. In particular, the invention relates to a magnetic disk drive for reducing the recovery time from the stopped or halted condition of the spindle motor to a rotational speed at which read and write can be performed.
2. Description of the Related Art
A head of a magnetic disk drive moves in the radial direction during rotation of the disk, and is accurately positioned to a target data track for performing read and write of information magnetically. FIG. 1 shows a sectional diagram of the configuration of a typical magnetic disk drive, which includes six heads 11, three disks 12-1, 12-2, 12-3 and a rotary actuator 13 that are stored in an enclosure. The heads 11 are supported by the rotary actuator 13 and are driven by a voice coil motor 14. Read and write are performed on both sides of the disks 12-1, 12-2 and 12-3, respectively. A package board 17 having the main part of the electronic circuits for controlling the magnetic disk drive is placed outside of the enclosure.
FIG. 2 shows a plan view indicating a configuration of an enclosure of a magnetic disk drive. A disk 12 rotates around an axis A in the direction indicated by an arrow, at the speed of several thousand rotations per minute. A rotary actuator 13 is driven by a voice coil motor, performs a reciprocating rotation motion pivotally around a position B and can move head 11 in the radial direction of the disk 12 as indicated by an arrow. Head preamplifier 15 for read and write, which is a part of the electronic circuits are not placed on a package board 17 of FIG. 1, is shown in this figure.
FIG. 3 shows a partial plan view of a magnetic disk drive including a data track 16, a magnetic disk 12 and a head 11 of a rotary actuator 13. Servo information for representing the positioning information of the head 11 is written on the magnetic disk 12 beforehand, for example at the factory. The electric power supplied to the voice coil motor is based upon the positioning information and is regulated to achieve accurate positioning of the head 11 for a target track 16 which is performed via a rotary actuator 13. The head positioning process for the target track is called a following operation. While the following operation is performed, the read and write of information are performed magnetically. Although tracks 16-1, 16-2, 16-3, 16-4 and 16-5 are indicated respectively by a solid line in FIG. 3, these tracks 16-1 through 16-S are produced by magnetic information and cannot be recognized optically. Since these tracks number more than ten thousand on the disk 12, the tracks have a much greater density than as shown in FIG. 3.
An operation for halting or stopping the rotation of the spindle motor for the purpose of reducing power consumption of the magnetic disk drive is widely employed in portable computers. For instance, the ATA interface standard standardized in X39.2 of ANSI sets forth an automatic power down sequence as a standard. According to this standard, the spindle motor is automatically halted and the power consumption is reduced when a data transfer request does not occur within a time predetermined by the user in a stand-by timer.
FIG. 4 shows a time chart of an automatic power down sequence. At first the disk is stopped in a stand-by status 40 and a host machine issues a command 35 for a magnetic disk drive to start rotation of a disk. In response, the magnetic disk drive performs the start of disk spin-up 30. The time it takes for increasing rotation of the disk is a process waiting time 37 and a status beginning from an end of the disk spin-up 31 is called an active status 41. Since the magnetic disk drive can perform read and write of data only in the active status 41, a command issued from the host machine is implemented in an execution time 38 as shown in FIG. 4. If the host machine does not issue an instruction after the issuance of the instruction 35 before elapse of the stand-by timer setting time, the start of disk spin-down 32 is executed to achieve stand-by status 42 at the end of disk spin down 33 Then, another start of disk spin-up 34 is executed when a command 36 is issued by the host processor. The process of issuing a command 35 and a next command 36 is a repetitive one.
FIG. 5 shows a time chart detailing the process from issuing a command 35 to waiting time 37 and execution time 38, as shown in FIG. 4. In an initial processing 52 soon after receiving the issuance of a read command 51 from the host machine, an interface circuit performs an instruction analysis, a system clock is initiated and a microprocessor is started up. Thereafter, there is the start of disk spin-up 68 for applying electric power to the spindle motor. Start-up rotation continues through a disk spin-up sequence 53 to an end of disk spin-up 69. At this time, a disturbance measurement 54 is performed for compensating for a disturbance added to an actuator in performing seek accurately. A main cause of the disturbance resides in the non-uniform wiring for a head mounted on the actuator or a voice coil motor and a non-uniform magnetic field in the magnet. Because the disturbance is influenced by the angle of the actuator or the ambient temperature, it is preferable to measure the disturbance under the circumstance where the hard disk drive is normally used. In an actual measurement, a method for repeating a dummy seek several times at different radial positions on the disk is often used and usually a method for performing the dummy seek not only at the time of starting up the disk but also at constant time intervals is employed in general. A seek 55 for a target track is performed after the disturbance measurement is performed. An actual read execution 56 is performed and the process moves to an end of the read command 57 after an end of the seek is confirmed. The time for the process from the issuance of the write command 61 to the end of execution of the write command 67 is the same as the time for the process from the issuance of read command 51 to the end of execution of the read command 57.
The time from the issuance of the read command 51 or the issuance of the write command 61 for the magnetic disk drive when it is in a stand-by status to the end of execution of the read command 57 or the end of execution of the write command 67 includes the time for the disk spin-up sequences 53 or 63 which are longer than the actual execution time for the read and write 56, 66. For data having 256 sectors, and for a magnetic disk drive using a glass disk approximately 63 mm in diameter which is typically used in a portable PC, the time for the read execution 56 and the write execution 66 is approximately 30 ms. Further, the time for performing the disk spin-up sequences 53 or 63 is approximately 1500 ms.